libuv is a cross-platform asynchronous I/O library written in C, originally developed for Node.js. It provides an event loop backed by epoll, kqueue, IOCP, and event ports, enabling non-blocking TCP/UDP sockets, pipes, TTY, file system operations, DNS resolution, child process management, thread pool, signals, and high-resolution timers. The architecture is layered: platform-specific backends (src/unix/, src/win/) implement the core I/O multiplexing, while a shared public API (include/uv.h) exposes handles, requests, and callbacks. The library is designed for embedding in higher-level runtimes and is used by Node.js, Luvit, Julia, and uvloop. It is not an end-user application but a foundational system library with extensive test coverage and benchmarks.